1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copier, a printer, a plotter, a facsimile, and a complex machine combining these device, etc., having a unique fixing system.
2. Discussion of the Background Art
Conventionally, in an image forming apparatus, such as a copier, a printer, etc., a fixing device is included to fix a toner image transferred onto a recording member. To avoid insufficient fixing, various fixing systems have been developed. In these days, a heat-applying roller that applies heat from a heat-applying source is generally used as a fixing roller, while a pressure-applying roller is provided opposing the fixing roller to form a nip in a heat roller system. Then, an unfixed image is cooperatively fixed onto the recording member by the fixing roller and the pressure-applying roller. A typical example of a conventional fixing device as the heat roller system includes a fixing roller 91 that applies heat to melt toner on the recording member and a pressure applying roller 92 that pressure contacts the fixing roller 91 to pinch the recording member as shown in FIG. 45. The fixing roller 91 is a cylindrical and includes a heat generation member 93 as a heat-applying source around a central axis thereof. The heat generation member 93 includes a halogen lamp or the like and generates heat upon receiving a prescribed power supply. Since the heat generation member 93 is positioned at the central axis of the fixing roller 91, an outer wall of the fixing roller is heated up to 150 to 200 degree centigrade appropriate for fixing. The fixing roller 91 and the pressure applying roller 92 rotate reversely and pinch a recording member having toner attracted thereonto in this situation while contacting each other. Then, the toner on the recording member is fused by the heat and fixed thereon at the nip between the fixing roller 91 and the pressure-applying roller 92.
In a typical prior art of a fixing device having the similar configuration, a recording member carrying a toner image passes through a fixing roller while receiving heat and a pressure applying roller are arranged, so that the toner image can be fixed onto the recording member as shown in the Japanese Patent Application Laid Open No. 2007-128109. However, such a fixing device simply including a heat applying system of the fixing roller consumes significant amount of energy. Because, fixing energy largely relies on heat as a problem. In addition, it especially takes a relatively long time period to increase temperature of the fixing roller suitable for fixing after a power is supplied to an image forming apparatus. Further, the above-mentioned fixing system has some disadvantages when employed in an image forming apparatus capable of feeding sheets at a high line speed. First, since the heat and pressure are simultaneously applied to the toner on the recording member at the nip, a sufficient nipping time period is hardly provided not to cause a fixing error. Thus, when the above-mentioned fixing system is applied to the high-speed machine running at the high-line speed, fixing temperature and pressure of the fixing roller need to be high and large to handle, resulting in significant power consumption.
Further, since the high-speed machine necessarily employs a fixing roller having a large diameter to obtain a nipping time period or the like, calorie increases so that power consumption further increases.
Further, since heat excessive for toner fixing is applied to a non-image area on the recording member, curl or the other undesired phenomena occur on the recording member.
As a fixing apparatus capable of resolving such a problem, the Japanese Patent Application Laid Open No. 58-178385 proposes an induction heat applying fixing apparatus that arranges a core (an open magnetic path iron core) winding a coil around a common axis in a fixing member made of metal. The apparatus flows a high frequency current through the coil and creates a high frequency magnetic field that causes induction heat. Since the fixing member made of metal conductor itself generates heat, it rapidly increases temperature in comparison with a system using a heat generation member, such as a halogen lamp, etc., and has heat efficiency as an advantage. Further, the Japanese Patent Application Laid Open No. Hei 9-80939 proposes a heat applying device included in an image forming apparatus that includes an exciting coil secured to a body, a film having a conductive layer traveling a magnetic field created by the exciting coil, and a heat applying device that pressure contacts an heat application objective against the film, while applying the heat thereto using a eddy current created on the conductive layer of the film to form an image using magnetic toner. The heat-applying device is characterized in that a magnetic field is created downstream in the rotational direction of the film within the section in which the film and the heat-receiving member contact each other to heat the heat-receiving member.
However, according to these configurations, since toner is heated by the magnetic field generation source via the fixing roller or the like serving as a heat-receiving member, heat efficiency is low and consumption of energy increases.
Further, the Japanese Patent Application Laid Open No. 2000-188177 proposes an electromagnetic induction heat applying apparatus having an electromagnetic induction heat applying layer that applies heat to a heat applying objective, in which a magnetic core made of magnetic material are arranged opposing the electromagnetic heat induction layer, and, a movable core capable of changing intensity of alternating magnetic field penetrating the electromagnetic heat induction layer are wound around the magnetic core.